1. Field of the Invention
The present invention relates to a control apparatus installed in a vehicle for controlling a device, such as an engine, installed in the vehicle. In particular, the present invention relates to the control apparatus that is capable of communicating with at least one other unit through a communication line.
2. Description of the Related Art
In a conventional vehicle, such as an automobile, an in-vehicle LAN (Local Area Network) composed of a plurality of communication lines is provided in the vehicle, and a plurality of electronic control units (ECUs) are also installed in the vehicle to be communicably coupled to the communication lines of the in-vehicle LAN. The ECUs communicate with one another through the in-vehicle LAN so that they control various types of devices installed in the vehicle.
One of the communication systems using the in-vehicle LAN adopts a predetermined communication procedure such that, when at least one ECU receives a command from at least one of the other ECUs, at least one of the ECU sends response data against the received command to at least one of the other ECUs through the in-vehicle LAN.
An external diagnostic scan tool can be communicably coupled to the communication lines of the in-vehicle LAN. The diagnostic scan tool is operative to diagnose the condition of a vehicle at a predetermined location, such as a vehicle maintenance shop. For example, when diagnosing a specific ECU that controls the engine of the vehicle in the ECUs, which is referred to as “engine ECU”, the diagnostic scan tool is set to establish communication with the specific ECU and sends a request thereto. The request is to output data representing the current engine state, such as the temperature of engine cooling water, the revolutions of the engine, and the like, and/or data representing the location of a fault.
The engine ECU receives the request transmitted from the diagnostic scan tool and sends data that is stored therein and corresponds to the request to the diagnostic scan tool as response data.
These communications between an ECU and the diagnostic scan tool are referred to as “diagnostic communications”. Response characteristics of the ECU to specific requests used for the diagnostic communications, such as time elapsed from the reception of the specific requests by the ECU to the start of transmitting response data with respect to the received specific requests, have already been established by the laws, such as ISO (International Organization for Standardization) 15031-5 or ISO 15765-4.
Moreover, when receiving requests transmitted from other ECUs, each conventional vehicle-installed ECU is configured to transmit pieces of data to all of the other ECUs at the same timings.
On the other hand, Japanese Unexamined Patent Publication NO. H11-201872 discloses a vehicle-installed system having a plurality of ECUs and a transponder unit that are communicable with each other through a communication line. Each of the ECUs is configured to diagnose vehicle-installed devices and to transmit the diagnostic results to a control center located at the exterior of the vehicle in response to the request.
In this system, each of the ECUs is operative to determine whether a period during which its load required for controlling the devices is higher than a predetermined amount occurs, and to ignore, when the period occurs, the request to transmit the diagnostic results during the period.
When each of the conventional ECUs installed in a vehicle receives requests transmitted from other ECUs installed therein, each of the conventional ECUs is configured to transmit pieces of response data corresponding to the requests to all of the other ECUs, respectively,
When requests are transmitted from other ECUs, each ECU installed therein is configured to transmit pieces of data, in response to the requests, to all of the other ECUs, respectively. The responsiveness of each of the conventional ECUs with respect to the other ECU's requests are identical with those thereof with respect to the specified requests, which meet the response characteristics established by the laws set forth above. This may cause processing loads of each of the conventional ECUs to increase.
In the engine ECU, for example, it is assumed that the engine ECU receives the requests transmitted from the other ECUs at the large engine-ECU loads, such as at high engine revolutions or at engine starting.
In this assumption, the responsiveness of the engine ECU for transmitting the pieces of response data with respect to the other ECU's requests may be identical with those thereof for transmitting pieces of response data with respect to the specified requests. This may result in that the large processing loads required for the transmitting of the pieces of the response data with respect to the other ECU's requests may be additionally applied on the engine ECU so that the engine ECU may skip a part of the engine control processes. This may require a high-performance processing unit as the engine ECU, as compared with the usual engine ECU.